Co2 Reactor venturi issue, excessive gas buildup

My reactor is set up with the dual venturi. It works pretty well, I'm using a Maxijet 900 (230gph). The issues:

1. Using the venturi, the pump will eventually "lock up," due to the air inside the impeller chamber. To solve for that, I put a second hole in the pump intake to vent the air as it builds up. Every hour or so, it "burps" and bubbles come out straight to the surface. This feels quite wasteful, as well as noisy when the pump begins to hold air.

2. When I'm not using the venturi, the chamber fills well over half way with bubbles, that's a ton of undissolved Co2. It does go away overnight, but that's a big chamber of Co2 being wasted.

Would you have any recommendations? Is the buildup due to the reactor size, or the strength of the pump? Reactor is about 14" long, top fed, 1.5" PVC. 32g tank, uncountable bubble rate.

Here's the system:

You can see the small notch in the intake area where the gas releases, it's in the little grate attachment just ahead of the venturi line.

The Co2 isn't injected into the powerhead directly, it comes from the upper part of the reactor, based on Tom's dual venturi design. The idea is to disperse the Co2 that usually builds up in the chamber as a mist in the tank. I measure Co2 by the reduction in Ph, over the course of the day it drops a solid 1.4 Ph. This is my first reactor.

Quite frankly, I'm having trouble seeing how this is more efficient than an inline atomizer, as it blows the same amount of mist with this design, and makes a lot more noise, lol. I'm guessing I just made the reactor chamber too small? Or set the venturi too high up in the chamber?

Is this a common problem with reactors? Do they get to a point where you are basically at a saturation point and they just fill up with gas? Is the only solution a bigger unit?

Lifetime Member

I'm not sure its really a saturation point as much as the gas injection rate exceeds the dissolution rate of CO2 within the reactor. You can improve dissolution rates a number of ways: increased flow (optimal counter current type flow), decreased bubble sizes, mechanical ways of breaking up the gas or preventing it from collecting all together. When the gas collects there is less surface area contacting the water so reduced dissolution of the gas. Basically everything is going for maximum mixing and minimum bubble size.

I like the cerges reactor styles, because I think you have more options to do these things within them. For example, Aquariumplants.com sells a cerges style reactor they put a pump into. The pump circulates water from the bottom into the top of the reactor. The added flow greatly enhances the efficiency of the reactor. Other commercial style reactors use spinning parts at the top to constantly chop up the collecting bubbles, most of these are versions of the Cerges design. In the types you are using people often add bio balls or other types of media to break up the bubbles and allow small bubbles to collect within the media. Something like that may help improve efficiency.

I've been thinking about the idea of adding a small plastic fan blade around a small cylinder that runs the length of the reactor. It would spin with the flow and break up bubbles. Not sure if it could be DIY'd since finding parts might be tough and putting it together more difficult.

I'm not sure if you could make the pump thing work in a reactor like this, but it would be interesting to see, since no one has done it that I'm aware of. You need a cable gland connector of the appropriate size for the pump cord. Cut the cord, drill a hole in the bottom side of the reactor the appropriate size for the cable gland connector, fix the pump inside (small rio) so that it flows counter to the inflow creating more stirring and agitation, run the cut cord through the gland and seal, reconnect the plug to the cord, and then seal up the reactor. This is all in theory and easier said than done...but it'd be cool to see a counter current pump inside a vertical style reactor like this. Basically same thing aquariumplants.com does...but in a different style reactor.

You can get too much flow through and carry out the bubbles before they are dissolved, but looking at the pump you are running, I'd say its underpowered for the size of your reactor. I use a very similar model on my large UV filter when I use it because the flow is slow and I get good dwell time. I wouldn't want that slow of a flow in a reactor. To start you could probably use a stronger pump, if you start to get a lot of bubbles moving out of the reactor through the outflow, a bit of media like coarse filter sponge in the bottom to collect the small bubbles would alleviate that.

Well, I went ahead and scrapped that reactor design and built one according to Tom's specs. I got that other design from another website, while it may have been perfect for a smaller tank, it wasn't able to handle the Co2 I needed to throw at it. The new one:

I used larger 2" tubing, and retained the full length, essentially doubling the chamber size of the old reactor. I am also feeding the Co2 into a tube reaching the bottom instead of in the nozzle on top. The venturi line penetrates about 3" into the reactor, allowing a small chamber to fill before it starts to "recycle" excess gas. To reduce the noise, this one is in my cabinet as opposed to behind the tank.

So far, this thing is a beast and can handle all the Co2 I throw at it. The diffusion rate is much better, I had to turn the Co2 down rather than up to dial in the amount I wanted. I'm much more of a believer now.

The old reactor was simply too small; it couldn't handle enough flow for the amount of Co2 I was using. Making things larger and optimizing the feed really improved that whole unit, and it's pretty slick now.

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